1. FIELD OF THE INVENTION
The invention relates to an improved inflatable packer or bridge plug for use in subterranean wells.
2. SUMMARY OF THE PRIOR ART
Inflatable packers (or bridge plugs) have long been utilized in subterranean wells. Such inflatable tools normally comprise an elastomeric sleeve element mounted in surrounding relationship to a tubular body portion. Pressured fluid is communicated from the surface of the well to the bore of the tubular body and thence through radial passages to the interior of an inner elastomeric sleeve. Such inner elastomeric sleeve is completely surrounded and secured relative to a plurality of peripherally overlapping, resilient, reinforcing slats or ribs. The medial portions of the reinforcing ribs are surrounded and bonded to an outer annular elastomeric packing element of substantially greater wall thickness. Normally, an upper securing assembly wedgingly engages the upper end of the inner elastomeric sleeve with the reinforcing slats and are fixedly and sealably secured relative to the central tubular body, while a lower securing assembly i sealably secured to a sealing sub which is mounted for slidable and sealable movements on the exterior of the central tubular body, in response to the inflation forces. A structure of this general type is shown in U.S. Pat. No. 3,160,211 to MALONE.
With inflatable tools of this type, it has been observed that the upper end of the reinforced inner elastomeric sleeve was expanding prior to the medial cover portions and becoming deformed, resulting in high local stresses. Such deformation occurs because the uncovered anchor ends of the inner elastomeric sleeve element expands with much less pressure than the medial portions of such sleeve element which are reinforced against expansion by the thick walled elastomeric packing sleeve. Such premature expansion of the upper end of the inflatable elements of the prior art inflatable packers resulted in an inward movement of the opposite end of the elastomeric cover sleeve, forcing the inner elastomeric sleeve into sealing relationship with the exterior of the tubular central body and thus preventing passage of the pressured fluid employed for expanding the inflatable inner elastomeric sleeve from reaching the lower portions of such sleeve. A further reason for the premature expansion of the upper end of the inner elastomeric sleeve of the inflatable packing assemblage lies in the fact that any inflation movement of the lower portions of the inflatable elements results in an immediate axial displacement of the lower securing assembly relative to the stationary tubular central body. Thus, the stress in the lower portions of the packing assemblage is substantially relieved by such axial movement, while the fluid pressure works on the upper portion of the inner elastomeric sleeve to deform it radially outwardly.
It has also been observed that both the upper and lower end portions of the inner sleeve expand prior to the medial portions, thus causing fluid to be trapped around the cover sleeve. Subsequent leakage of such trapped fluid will permit the cover to expand, reducing the inflation pressure and setting the stage for fluid leakage past the cover element.